Test are most important for testing water and the the test will be having in three states like physical tests,chemical test and bacteriological test.The test are conducted in temperature and taste and odour.the water will be tested in the three process.The main process is the physical process it is also a natural process.By the odour is we can know the taste of the water and micro organisms in the water.By increasing the water temperature it will kill the micro organisms.
Physical tests includes the following:
1.Temperature
Temperature is measured by means of ordinary thermometer.The temperature of surface water generally equal to that of atmosphere.The temperature of ground water may be more or less than the atmosphere,most desirable temperature for public supply is 4.4 to 10°c.Temperatur above 26°c undesirable and above 35°c is unfit for supply.The parameters has no much significant as it is not used possible to control temperature in public water supply system.
2.Taste and odour:
Taste and odour of water are usually closely related to some extent subjective parameters.The are caused due to dissolved organic matter,micro organisms either dead or live, inorganic salts, dissolved gases,excess chlorination during treatment, reactions with asphaltic and bitumers coating of pipes, pollution by industrial water.
The intensity of odour is measured by osmoscope terms of "Threshold number".The threshold number is the dilution ratio at which odour is just detectable.For example if 10c.c. of water sample has to be added to 100c.c. of distilled water to produce detectable odour then the threshold number of the sample is 10.
The presence of salts like sodium chloride render brackish taste.Sulphates in water give slightly sweet taste.The potable water should be not possess any objectionable odour or taste and the threshold number should not be greater than 3.
3.Turbidity:
Turbidity is a measure of the resistance of water to the passage of light through it and is due to the presence of a.suspended and collidial mineral matter like clay silt etc. b.Living or dead algae and other organisms turbidity depends on the types of soil over which the water has to run and velocity of water.Turbidity is measured in ppm or by weight of suspended matter in water.For water,the unit ppm and mg/1 at approximately equal.Turbidity was previous determined by Jackson candle turbidity units.The unit is now being replaced by more appropriate unit called "Nephelometric turbidity unit.
The turbidity produced by one milligram of finely divided silica mixed in one litre of distilled water,is the standard unit.The turbidity is measured by
a.Turbidity rod:
It consists of a graduated aluminium rod,the upper end of which is attached to a similarly graduated non stretchable tape.At the lower end of the rod,a platinum neddle of 1mm dia,and 25mm length is fixed.While viewing from upper end of the tape the rod is dipped in water slowly until the platinum neddle just disappear.The reading at the water surface is taken which directly given in the turbidity.
b.Jackson turbidmeter:
It is used to measure turbidity directly in the range 2 to 1000 mg/ 1 or more.It consists of a metal stand on which a metal containing supporting a calibrated glass tube placed.A stranded candle is placed below the metal tube.Water is added gradually to the glass tube until the image of candle flame cases to appear when see from the top of the glass tube.The reading corresponding to the depth of the water in glass tube is directly gives the values of turbidity of the sample.
Low concentrations of turbidity can be measured accurately by means of a.Baylis turbidmeter b.Hellig turbidmeter c.self reading turbidmeter d.Hach laboratory turbidmeter based on Nephelometric method.
4.Colour:
Colour is due to collidial and dissolved solids of certiar organic and inorganic. colour in potable water undesirable in aesthetic point in view through it has little sanitary significance.The colour of water is usually experienced in Hazen units which are the same as the platinum cobalt scale.Before testing the sample suspended matter is removed by centrifuging.After this is the colour of water compounds with the standard colour solutions in nessle tube or colour discs.
The standard unit of colour is fixed at that produced 1mg of platinum cobalt in a little of water.The number of the platinum cobalt scale should not be execed 25 as should be preferable less than 5 for potable water.
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